This invention relates to the technology of liquid-crystal display apparatus, more particularly, to a liquid-crystal display apparatus capable of producing high-contrast image over a wide range of viewing angles.
The use of liquid-crystal displays (LCDS) as a display for word processors and computers is rapidly increasing today. The use of LCDs as a monitor in ultrasonic, CT and MRI diagnostic apparatus is under review. Conventionally, these medical diagnostic apparatus have primarily used CRT-s (cathode-ray tubes) as a monitor.
LCDs have many advantages such as ease in size reduction, small thickness and lightweightness. On the other hand, they have poor viewing angle characteristics (narrow viewing angle) since as the viewing direction or angle changes, the contrast of an image decreases sharply and the gradation also reverses to have the image look differently. As a result, depending on the position of the viewer, the image cannot be viewed correctly.
In the medical applications described above, correct viewing of images is important particularly for preventing wrong diagnosis. What is more, diagnosis based on the difference in image density requires that images of high contrast ratio be displayed over a wide range of viewing angles. Another problem peculiar to medical monitors is that image is usually displayed in monochrome (black and white colors) and, hence, suffers considerable drop in contrast as the viewing angle varies.
A known method for increasing the viewing angle of LCDs relies upon using collimated backlight and the image-bearing light that has passed through the liquid-crystal display panel is diffused with a diffusing plate. This method increases the viewing angle of the liquid-crystal display panel and enables the fabrication of an LCD that produces high-contrast image display over a wide range of viewing angles.
A problem with this method is that uneven display or blurred image may occur if the collimated light and the liquid-crystal display panel do not match in characteristics. For example, if the average pitch of outgoing collimated light is larger than the pixel size of the liquid-crystal display panel, the backlight is incident in different quantities on the pixels of the liquid-crystal display panel, producing unevenness in the image being displayed.
Since incorrect recognition of an image can cause wrong diagnosis or inconsistency in the results of diagnosis, uneven display and blurred image are particularly serious problems in the medical applications.
The present invention has been accomplished under these circumstances and has as an object providing a liquid-crystal display apparatus that uses collimated backlight in combination with a light diffusing plate in order to display high-contrast image over a wide range of viewing angles and which yet can display high-quality image without unevenness and blur that would otherwise result from a mismatch between the characteristics of collimated light and the liquid-crystal display panel adapted to have an increased range of viewing angles.
In short, by using the liquid-crystal display apparatus of the invention, high-quality images that are free from unevenness and blurring can be displayed with high contrast over a wide range of viewing angles.
In order to attain the object described above, the first aspect of the present invention provides a liquid-crystal display apparatus having a liquid-crystal display panel and a backlight section that uses a collimating plate to have collimated light launched into the liquid-crystal display panel, the apparatus satisfying the following relation:
p/tan xcex8xe2x89xa6L
where p is an average pitch of emergence of the collimated light, xcex8 is a divergence angle of the collimated light, and L is a distance from the collimating plate to an interface in a liquid-crystal layer of the liquid-crystal display panel which is directed to the collimating plate.
The second aspect of the present invention provides a liquid-crystal display apparatus having a liquid-crystal display panel, a backlight section that uses a collimating plate to have collimated light launched into the liquid-crystal display panel and a light diffusing plate that diffuses the image-bearing light that has passed through the liquid-crystal display panel, the apparatus satisfying the following relation:
dxc3x97tan xcex8xe2x89xa6A
where xcex8 is a divergence angle of the collimated light, d is a distance from the light diffusing plate to an interface in a liquid-crystal layer of the liquid-crystal display panel which is directed to the light diffusing plate, and A is a pixel size of the liquid-crystal display panel.
The third aspect of the present invention provides a liquid-crystal display apparatus having a liquid-crystal display panel, a backlight section that uses a collimating plate to have collimated light launched into the liquid-crystal display panel and a light diffusing plate that diffuses the image-bearing light that has passed through the liquid-crystal display panel, the apparatus satisfying the following relations:
p/tan xcex8xe2x89xa6L
dxc3x97tan xcex8xe2x89xa6A
where p is an average pitch of emergence of the collimated light, xcex8 is a divergence angle of the collimated light, L is a distance from the collimating plate to an interface in a liquid-crystal layer of the liquid-crystal display panel which is directed to the collimating plate, d is a distance from the light diffusing plate to the interface in the liquid-crystal layer of the liquid-crystal display panel which is directed to the light diffusing plate, and A is a pixel size of the liquid-crystal display panel.
In the liquid-crystal display apparatus according to each aspect of the present invention, it is preferable that the backlight section has not only the collimating plate but also a light source and a lamp housing for accommodating the light source an inner surface of which is covered with a diffuse reflecting layer, and the collimating plate has a lens substrate, a multiple of lenses that are supported on the lens substrate for collimating incident light, a diffuse reflecting layer that is formed over the lens substrate except in light entrance areas that align with an optical axes of the lenses, and a shield layer that is formed over the lens substrate on a | side closer to the lenses than the diffuse reflecting layer except in the light entrance areas.
It is also preferable that the pixel size of the liquid-crystal display panel is no more than 200 xcexcm.
It is another preferable that the collimated light has a divergence angle xcex8 of no more than xc2x110xc2x0.
It is further preferable that the liquid-crystal display panel is monochromatic.